The present disclosure relates to marking engines within electrostatographic printing or xerography systems. Specifically this disclosure relates to a charging device that may be used in a marking engine within a xerographic system.
In electrostatographic systems, a photoreceptor may be supported by a mechanical carrier such as a drum or a belt. The photoreceptor may be charged to a generally uniform charge by subjecting the photoreceptor to a suitable charging device. The charge distribution on the photoreceptor may then be altered by the application of radiation, e.g., a laser, to the surface of the photoreceptor. Toner particles may then be transferred, by the application of electric charge, to a print sheet, thus forming the desired image on the print sheet. The toner particles adhere electrostatically to the suitably charged portions of the photoreceptor. An electric charge may also be used to separate or “detack” the print sheet from the photoreceptor.
For the initial charging, transfer, or detack of an imaging surface, the most typical device for applying a predetermined charge to the imaging surface may be a “corotron,” such as a scorotron or dicorotron. Common to most types of corotron may be a bare conductor, in proximity to the imaging surface, which may be electrically biased and thereby supplies ions for charging the imaging surface. The conductor typically comprises one or more wires (often called a “corona wire”) and/or a metal bar forming saw-teeth (a “pin array”). The conductor may extend parallel to the imaging surface and along a direction perpendicular to a direction of motion of the imaging surface. Other structures, such as a grid, conductive shield and/or nonconductive housing, are typically present in a charging device, and some of these may be electrically biased as well. A corotron having a grid disposed between the conductor and the photoreceptor is typically known as a “scorotron.”
U.S. Pat. No. 5,845,179, incorporated by reference in its entirety, discloses design rules for a corotron, with the objective of minimizing the production of ozone, which may detract from charge uniformity.
U.S. Pat. No. 6,459,873, incorporated by reference in its entirety, discloses a xerographic charging device apparatus having two independently controllable scorotrons.
Monochrome printers produce a hard copy in one toner color, typically black, and the copy may be made in a single pass of the charging device and toner source over the photoreceptor.
On the other hand, color printers may use three primary colors, typically cyan, magenta and yellow, and in addition, optionally black. Several techniques have been developed over the years to adapt xerographic techniques to use multiple colors.
An exemplary apparatus for making high quality color prints by xerographic systems is discussed in U.S. Pat. No. 4,728,983, incorporated by reference in its entirety. A single photoconductive drum may be electrostatically charged, laser-scan exposed, and toner developed during one rotation. In successive rotations, different colored images corresponding to color separation images may be assembled in registration on the drum. This assembled color image may be transferred to a receptor sheet in a final rotation of the drum.
Advancements in xerographic technology include tandem color marking engines, which comprise a plurality of charging devices. Such devices may be suitable for high-speed applications and have been developed for both photoconductive drums and belt systems.